The present invention relates to a laminate-type gasket such as a cylinder head gasket which is held between a cylinder head and a cylinder block of an engine and seals therebetween, or an exhaust manifold gasket which is held between an exhaust manifold and an exhaust pipe and seals therebetween.
In an automobile engine, the laminate-type gasket such as the cylinder head gasket or the exhaust manifold gasket is used. The cylinder head gasket is held between engine members such as the cylinder head and the cylinder block (cylinder body) and the like, tightened by head belts, and seals fluid such as combustion gas, oil, coolant water and the like. The exhaust manifold gasket is held between the exhaust manifold and the exhaust pipe, and seals the combustion gas.
On the other hand, the laminate-type gasket includes secondary sealing-target holes such as bolt holes and the like for attaching the laminate-type gasket to an engine member besides main sealing-target holes such as cylinder bores and the like. In a conventional technology, the engine member was made of cast iron, so that a fastening force could increase without deforming the sealing-target holes. Also, pressure of the combustion gas of the engine was relatively low, and required sealing performance was low, so that even sealing performance around the bolt holes did not have any special problem.
However, due to a lightweight and high power engine, recently, the engine member is made of aluminum alloy, so that rigidity has declined and an indentation due to tightening can easily occur. Accordingly, high sealing performance is required. However, it is difficult to increase the fastening force. Moreover, when an unequal force is applied to a contact surface of the gasket, the sealing-target holes such as the cylinder bores and the like on an engine member side may be deformed.
Among the above-mentioned laminate-type gaskets, as shown in FIGS. 7 and 8, there is a laminate-type gasket 1X wherein a first metal substrate 10 provides a folded portion 12 on a peripheral border portion of a main sealing-target hole 2, and wherein bead plates 30X with full beads 31 for the main sealing-target holes 2 are placed inside the folded portions 12. In the laminate-type gasket 1X including the bead plates 30X, the bead plates 30X are placed only around the main sealing-target holes 2, so that, as shown in FIG. 7, the bead plates 30X are formed only on the peripheral border portions of the main sealing-target holes 2 in a circular shape. Incidentally, a cylinder head gasket, which includes the circular bead plates and is provided with full beads surrounding beads of the bead plates in the first metal substrate, is proposed (for example, refer to Japanese Patent Unexamined Publication No. 2003-139247).
In the above-described laminate-type gasket 1X, by applying a large pressing force near a bolt hole 3 by fastening a fastening bolt, the sealing performance of the bolt hole 3 which is the secondary sealing-target hole could be assured sufficiently. However, in a recent aluminum alloy engine, due to declined rigidity of the engine member, a large bolt fastening force cannot be applied. As a result, the sealing performance around the bolt hole 3 is difficult to be obtained. Moreover, the number of the metal structural plates on a sealing-target hole 2 side is greater than that around the bolt hole 3, so that a seal surface pressure on the sealing-target hole 2 side becomes larger than that around the bolt hole 3. As a result, the sealing-target hole 2 may be easily deformed.
The present invention is made in order to solve the problems described above, and an object of the present invention is to provide a laminate-type gasket such as the cylinder head gasket or the manifold gasket and the like, which are used for the engine, can improve the sealing performance of each sealing target hole, and can reduce deformation of members which hold the laminate-type gasket, such as the deformation of the cylinder bores.
Further objects and advantages of the invention will be apparent from the following description of the invention.